The present invention relates to air-pruning trays used to grow seedlings for transplanting, and in particular to air-pruning trays having a plurality of growing cells of an improved shape. The invention also pertains to air-pruning plant growing systems comprising the aforesaid trays in combination with an air permeable support tray.
In order to satisfy the demand for millions of healthy, uniform seedlings used in the production of tobacco, vegetables, forestry and horticultural plants, as well as to facilitate the automated transplanting of such seedlings, it has become the practice within the industry to produce seedlings under greenhouse conditions in plant trays containing a plurality of growing cells. After the seeds germinate and the seedlings have grown to transplanting size, they are removed from the cells, by hand or mechanical means, and planted in the soil or other final growing location.
One technique that has been found to be highly successful in the producing healthy seedlings of uniform size with a well developed root system is call air-pruning. In air-pruning, seedlings are grown in growing medium in cells which are open at the top and bottom. After the seeds germinate, the plant roots grow toward the bottom of the cell. When the roots reach the lower opening of the cell, they are exposed to air, and hindered. Secondary roots then develop, which also grow downward until reaching the air, and the cycle is repeated. As a result, the seedling develops an extensive system of downwardly extending roots, without root spiraling or root binding.
Normally, the air-pruning tray rests on a detachable bottom tray which has a screen or perforated bottom that fits against the bottom of the cells, preventing loss of the medium from the cells, while allowing air to contact the lower surface of the medium. When the seedlings are ready for transplanting, the bottom tray is separated from the air-pruning tray, and the seedling with its attached medium is removed, normally by pushing the plant and medium out of the cell bottom.
An example of a prior art air-pruning tray system is found in U.S. Pat. No. 5,179,800 to Huang. The system disclosed therein comprises a tray with a plurality of aligned and uniformly spaced, truncated pyramid shaped cells having an open top and an open bottom, and a detachable screen or perforated bottom tray. Each cell tapers upward from the open bottom. The open top of each cell edge has a small inward curl to facilitate the passage of plant shoots during transplanting.
The dimensions of an air-pruning trays are limited by the dimensions which are acceptable by automated transplanting machinery, as well as other factors such as ease of handling. As a result, the number of plant cells that can be incorporated into a tray is limited. Desirably, however, the tray will contain as many cells as possible to reduce the number of trays handled. Sufficient, but not excessive, growing medium and space should be available in each cell to allow for the development of an extensive root structure and a healthy seedling. Ideally, the growing medium can be easily packed to a uniform density within the cell, and the seedling and medium can be readily removed from the cell when the seedling is to be transplanted, without having a tendency to prematurely fall from the cell.